Ken, I believe other postings on this topic this weekend clearly show that electronic circuits which were not designed as radio receivers can possibly be interfered with by the emissions from products which meet FCC/CISPR 22 limits, for a number of possible reasons, especially when the product is closer than 10 metres to the source of the emissions.
Certain kinds of transducers and their amplifiers appear to be particularly at risk because of the low levels of their transducer signals. Regards, Keith Armstrong In a message dated 06/01/02 06:56:28 GMT Standard Time, ken.ja...@emccompliance.com writes: > Subj:Re: EMC-related safety issues > Date:06/01/02 06:56:28 GMT Standard Time > From: ken.ja...@emccompliance.com (Ken Javor) > To: cherryclo...@aol.com > CC: emc-p...@majordomo.ieee.org > > My point was that only radios are sensitive to rf fields at the levels > controlled by FCC/CISPR22 and indeed, as Ing. Gremen pointed out, levels > well above the limits. Which means that the only rationale behind > FCC/CISPR22 is protection of radio broadcast reception. Period. > > on 1/5/02 12:10 PM, cherryclo...@aol.com at cherryclo...@aol.com wrote: > > >> Dear Ken >> I am truly sorry if I irritated you by misunderstanding your words, but I >> took your posting to imply that electronic circuits which are not designed >> as RF receivers would not respond very well to radio frequencies. >> >> My example was not intended to be a full answer to your example (there are >> other postings which are dealing with that) just to indicate that the >> frequency response of slow and commonplace ICs can be very high indeed. >> >> I am sensitive to this issue because I keep on running across electronics >> designers who say things like: "I don't need to worry about the RF >> immunity of my audio amplifier/motor >> controller/temperature/pressure/flow/weight/velocity measurement and >> control system (please delete where applicable) because the opamps I use >> have a GBW of under 1MHz so they won't see the RF" ­ which is of >> course complete bollocks (a UK phrase that I hope translates well enough >> for all emc-pstc subscribers). >> >> And no, I still don't agree with you that only radio receivers are >> sensitive enough to RF to have a problem with what you are still calling >> 'unintentional emissions' (even though this term means very little in an >> international forum unless you define the relevant standards or laws). >> >> I think the problem you are concerned with is application dependant and we >> cannot make such broad assumptions. As I said earlier, most interference >> problems are caused by radio transmitters or radio receivers, but not all. >> >> Regards, Keith Armstrong >> >> In a message dated 05/01/02 01:20:27 GMT Standard Time, >> ken.ja...@emccompliance.com writes: >> >> >>> Subj:Re: EMC-related safety issues >>> Date:05/01/02 01:20:27 GMT Standard Time >>> From: ken.ja...@emccompliance.com (Ken Javor) >>> To: cherryclo...@aol.com, emc-p...@majordomo.ieee.org >>> >>> One sure way to REALLY irritate me is to twist my words and try to make >>> me look stupid (I do a fine job by myself on occasion and don't >>> appreciate any outside help). I did not say that pn junctions don't >>> detect and rectify rf, I said that the field intensities associated with >>> unintentional emissions from ITE are too low to cause susceptibility in >>> circuits other than radios. Your example here is 10 V/m, and you are >>> talking about an op-amp (gain unspecified) and that it was susceptible at >>> that level should be no surprise to anyone. >>> >>> on 1/4/02 7:34 AM, cherryclo...@aol.com at cherryclo...@aol.com wrote: >>> >>> >>>> Does anyone else think that ordinary semiconductors doesn't respond >>>> to RF? >>>> >>>> I have tested a product which was little more than an LM324 quad op-amp >>>> for RF immunity using IEC 61000-4-3. This op-amp has a slew rate of >>>> 1V/micro-second on a good day with the wind in its favour. It was housed >>>> in an unshielded plastic enclosure. >>>> >>>> Demodulated noise that exceeded the (not very tough) product >>>> specification were seen all the way up to 500MHz at a number of spot >>>> frequencies that appeared to be due to the natural resonances of the >>>> input and output cables. >>>> >>>> Above 500MHz this resonant behaviour vanished to be replaced by a >>>> steadily rising level of demodulated 1kHz tone as the frequency >>>> increased. I stopped testing at 1GHz, where the output error from the >>>> product was about 10% and still rising with increased frequency. >>>> >>>> OK, the field strength for the test was 10V/m (unmodulated) but the real >>>> surprise was how well this very cheap and very slow opamp demodulated >>>> the RF, and that it demodulated better at 1GHz than at 500MHz. >>>> >>>> I have done many many immunity tests using IEC 61000-4-3 on audio >>>> equipment and found much the same effects with every product I've ever >>>> tested. >>>> With most larger products there is usually a roll-off in the >>>> demodulation above 500MHz - not because the semiconductors in the ICs >>>> can't respond (they can) but apparently because larger products have >>>> higher losses above 500MHz or so between the cable ports and the >>>> semiconductors, plus a denser structure that might provide more >>>> self-screening. >>>> >>>> The transistors and diodes in all modern ICs (analog or digital) are so >>>> tiny that they make excellent detectors at UHF and beyond. As they get >>>> smaller (and they are) their frequency response increases (and their >>>> vulnerability to upset and damage decreases). >>>> >>>> Regards, Keith Armstrong >>>>
